Currently, ophthalmic lenses intended for correcting the ametropia of a wearer consist of a substrate with front and rear faces that have shapes suitable for providing the desired correction. To this purpose, semi-finished lens blanks are mass-produced in factories, with one of the faces of each blank possessing a definitive shape. The other face of each blank is subsequently machined individually according to the ametropia correction prescribed for the wearer, in intermediate laboratories between the factories and the lens sales outlets. Such an organization for the manufacture of ophthalmic lenses requires there to be, in each laboratory, stocks of several models of blanks according to the curvature of the face formed definitively during the production of the blank itself. Depending on the wearer's requirements, additional optical functions, such as for example an anti-reflection function, are added to each lens during separate treatments of the lenses, which consist in covering one or both faces thereof with functional coatings. Such treatments lengthen the timescale for delivering the lenses to the wearer. Finally, the blank is machined around an outline that corresponds to the housing in a frame for a pair of spectacles selected by the wearer, in order to obtain the lens that is fitted into the frame. For this purpose, the spectacle lens blanks each have a sufficient diameter, which is usually between 60 mm and 80 mm (millimeters).
Such an ophthalmic lens manufacturing process is inflexible in that there is no simple way of adding functions to the lens without requiring additional treatment steps to be carried out on the lens. Furthermore, the stocks of blanks that are held in each laboratory require an important and expensive management and logistics system.
In an attempt to remedy these drawbacks, it has been proposed to produce each lens in the form of a substrate on which one or more layers are formed that provide the lens with certain optical functions required by the future wearer thereof, such as an ametropia correction. The number of different substrate models needed to meet all the requirements of a population is then greatly reduced, since some of the characteristics specific to each wearer are produced by means of layers. These layers are produced on demand according to the wearer's prescription and additional optical functions as desired. One way of producing such a functionalized layer consists in irradiating different portions of the layer in a variable and selective manner, so as to vary the optical refractive index between different points on the surface of the lens. However, such a treatment of the layer for obtaining the characteristics specific to each wearer is lengthy to implement when it is carried out on an individual basis and does not allow a large number of different lenses to be rapidly produced one after another.
It is also known to provide certain functions to the lens, such as a polarizing power or an anti-reflection function for example, via a film that is produced independently of the substrate. The film is then attached to a substrate blank, for example by thermal bonding, and then the assembly is machined to the dimensions of the housing in the frame. One drawback of this type of process arises from the deformation that the film undergoes while it is being bonded to the substrate blank. Indeed wrinkles, stretches or tears may occur in the film during bonding.
Moreover, it is also known to produce the optical characteristics that are desired for a lens in the form of an array of separate cells juxtaposed on one of the faces of the lens. Each cell contains a functional material which, by this material varying between neighbouring cells, gives the lens the desired characteristics. For example, it is known in this way to give the lens an optical power by introducing materials having different optical refractive indices into the cells. It is also known to produce in this way a progressive lens or PAL (Progressive Addition Lens) by locally varying, on the lens, the materials contained in cells relative to a lens with cells having a constant optical power. The optical function of the lens is then written into the lens in the form of dots, usually called pixels. The film is then thermally bonded to the substrate. However, in such a process the operations of producing and filling the cells on the curved surface of the lens are difficult to implement.
One drawback of these processes lies in the difficulty in producing different lenses in a continuous and economic manner and with a level of quality suitable for ophthalmic applications.